As the Senate opens debate on gun control after a last-minute bipartisan deal, a review of legislation now before state lawmakers gives a striking evidence of how difficult it will be to enact restrictions on firearms into law, even given the political momentum such measures have received following the December shooting tragedy that left 26 people -- most of them young children -- dead at the Sandy Hook elementary school at Newtown, Conn.

A review of nearly 1,500 firearms-related bills introduced in the 50 state legislatures since the beginning of the year by Sunlight reveals that the post-Newtown push for stronger gun control has been countered by an almost equally vigorous effort on the other side. Barely half the bills would strengthen gun laws; the other half would weaken them.

Still, getting to parity with the anti-gun-control forces represents political progress for gun control advocates. Last year, just 35 percent of gun bills introduced in state legislatures would have strengthened regulations, according to the Law Center to Prevent Gun Violence; in 2011, the figure was 43 percent.

“This year, we've seen an increase in volume of legislation and an increase in the number of bills to strengthen gun laws (which are the majority of 2013 bills),” Ben Van Houten attorney with the Law Center said via email.

This trend though, is not a national one. Sunlight's analysis found that bills to strengthen regulations made up a significant majority of firearms-related legislation in only about 20 states; in the others, the majority of firearms-related bills would weaken gun laws, or the gun issue has not generated significant legislative activity. In the map above, the darker colors indicate the states where there has been the most gun-related legislation introduced. Click on the states for more information about the bills introduced there.

Legislative initiatives vis-a-vis guns in states run the gamut: There are bills to ban (or not) assault weapons; bills to tighten (or loosen) concealed carry provisions; bills to require (or not) background checks, and bills to prohibit (or allow) guns in schools. There also have been a number of bills introduced nullifying any future federal gun control regulations.

The 20 states where pro-gun control forces appear to have the upper hand include four where sweeping new regulations of firearms and ammunition have either already been enacted or are awaiting certain signatures by governors: